Validating an object exists when editing

This is extremely silly, but I can't for the life of me figure it out.

I want to validate that an Employee username doesn't already exist when adding or editing an Employee. Here's my view model:

public class EmployeeViewModel
{
    [ScaffoldColumn(false)]
    public int EmployeeId { get; set; }

    [Remote("UsernameExists", "Employees", ErrorMessage = "Username already exists")]
    public string Username { get; set; }
}

And in my controller:

public ActionResult UsernameExists(string username)
{
    return Json(!_employeesRepository.UsernameExists(username), JsonRequestBehavior.AllowGet);
}

The function in the employee repository:

public bool UsernameExists(stri开发者_运维技巧ng username)
{
    return Employees.Where(e => e.Username.ToLower().Equals(username.ToLower())).Count() > 0;
}

This works great when I'm creating an Employee. But if I'm editing one and I try to save it, I get an error that the username already exists (which is true). So I need to somehow tell the function that it's okay the username exists if I'm editing an Employee with that username.

Is this possible with remote validation?

Pass in a extra flag to indicate what mode you're in, e.g. bool isEditMode and based on that, tweak your results. You can use AdditionalFields attribute to pass in that info; Also, take a look here: Remote Validation in ASP.Net MVC 3: How to use AdditionalFields in Action Method

You can solve this problem by using two different viewmodels in which you derive the one from the other: the superclass can be used for editing, the subclass is for inserts with remote validation.

public class EmployeeViewModel // The normal one, can be used for editing
{
    [ScaffoldColumn(false)]
    public int EmployeeId { get; set; }

    public virtual string Username { get; set; }
}

public class InsertEmloyeeViewModel : EmployeeViewModel
{
    [Remote("UsernameExists", "Employees", ErrorMessage = "Username already exists")]
    public override string Username { get; set; }

}

When the edit-functionlity also contains some 'specialities', you could derive a third class 'EditEmployeeViewModel' from the base class EmployeeViewmodel.